Process for the manufacture of ductile metals in a finely-divided form



United States Patent Ofifice 3,236 631 PROCESS FOR THE MANIIFACTURE F DUCTILE METALS IN A FlNELY-DIVIDED FORM Karl-Georg Knaulf, Aachen, Germany, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed May 2, 1962, Ser. No. 191,706 Claims priority, application Germany, May 15, 1961, N 20,050 2 Claims. (Cl. 75-84) This invention relates to processes for the manufacture of a finely-divided powder from a ductile metal such as tantalum, niobium, vanadium, titanium and zirconium, which may be indicated as metals, which exothermally absorb hydrogen.

The said metals in a finely-divided form are good getter materials which may be used, for example in discharge tubes.

The surface area of the material is of decisive importance for non-evaporating getter materials since not only the getter capacity, but also the getter velocity increases with increasing surface.

The majority of metals, which are very suitable as nonevaporating getters because of their chemical properties, such as, for example, Ta, Nb, V, Ti and Zr, are frequently available in a very ductile form and cannot therefore be obtained in a finely-divided shake by merely grinding.

An object of the invention is to overcome this difiiculty. A process for obtaining ductile metals, such as Ta, Nb, V, Ti and Zr, in an extremely finely-divided form has been found which is characterized in that the grinding process is carried out in an atmosphere of hydrogen of very high purity.

The reasons for the fine-granular state of the resulting ground product are probably the following: During grinding first metal surfaces free of oxide are locally produced by mechanical action. These oxide-free parts of the metal react with the surrounding hydrogen while forming hydride phases at the surface. Now, the formation of hydride, more particularly with Ta, Nb, V, Ti and Zr, is accompanied by a considerable increase in volume, resulting in great stresses at the boundary surface of the hydride phases relative to the basic metal. The increase in volume is usually from to 20%. Moreover the hydrides of these metals are very brittle in mechanical respect. The stressed condition at the surface and brittleness, together with the mechanical load during grinding,

3,236,631 Patented Feb. 22, 1966 give rise to very fine particles of metal hydride being separated from the surface, whereafter the process is repeated until the whole of the metal is converted into hydride and available in extremely finely-divided form.

By heating in vacuo, which in the manufacture of discharge tubes may preferably be effected after providing the hydride on the electrodes, the hydrogen may be completely extracted again from the hydrides, thus obtaining the pure metal in a very finely-divided state.

The grinding process is preferably carried out in a vibrating mill containing steel balls and closed in a gastight manner. The pure hydrogen required may be supplied through a tubing of, for example, diffusion-tight butyl rubber.

The process has been found satisfactory more particularly with titanium and zirconium.

When zirconium was ground in this way for about 1 hour, a powder was obtained after heating in vacuo to 500 C., the BET-surface area of which was 5.5 m. g. The surface was measured as described in Journal of the American Chemical Society, 60, 309 (1938).

What is claimed is:

1. A process for the manufacture of a finely-divided powder from a ductile metal which absorbs hydrogen at ambient temperature comprising the steps, grinding the ductile metal in an atmosphere of substantially pure hydrogen to reduce the ductile metal to a finely-divided metal hydride, and thereafter heating the so-formed metal hydride in vacuum to form the finely-divided metal powder.

2. A process for the manufacture of a finely-divided powder from a metal selected from the group consisting of tantalum, niobium, vanadium, titanium and zirconium comprising the steps, grinding said metal in an atmosphere of substantially pure hydrogen to reduce the metal to a finely-divided metal hydride, and thereafter heating the so-formed metal hydride in vacuum to form the finely-divided metal powder.

References Cited by the Examiner UNITED STATES PATENTS 1,081,568 12/1913 Becket 84 1,602,542 10/ 1926 Marden 75-84 2,107,277 2/1938 Austin 75-84 2,905,547 9/1959 Yoblin 7584 CARL D. QUARFORTH, Primary Examiner. 

1. A PROCESS FOR THE MANUFACTURE OF A FINELY-DIVIDED POWDER FROM A DUCTILE METAL WHICH ABSORBS HYDROGEN AT AMBIENT TEMPERATURE COMPRISING THE STEPS, GRINDING THE DUCTILE METAL IN AN ATMOSPHERE OF SUBSTANTIALLY PURE HYDROGEN TO REDUCE THE DUCTILE METAL TO A FINELY-DIVIDED METAL HYDRIDE, AND THEREAFTER HEATING THE SO-FORMED METAL HYDRIDE IN VACUUM TO FORM THE FINELY-DIVIDED METAL POWDER. 